The disclosure relates to a mobile working machine, for example an excavator, a truck with a superstructure, or an agricultural and forestry device comprising at least one working arm. Working arms of such working machines usually have a plurality of segments interconnected in an articulated fashion, a tool such as a bucket, a gripper or a hammer being fitted on a segment, also called a shank.
The current position and attitude of the working arm and, in particular, also of the tool is frequently indicated to the operator of such a working machine on a display, the operator thereby being enabled to carry out work according to accurately prescribed plans, and receives direct feedback relating to achieved levels, lengths, depths or inclinations, for example of a bulk material or soil which has been moved, or of the underlying ground which is to be shaped or has already been shaped.
Such operator displays are known, for example, from DE 201 16 666 U1 and U.S. Pat. No. 5,854,988 A.
In this case, the position and the attitude of the tool are frequently determined, partly because of the good retrofitting possibility, by inclination sensors that are fitted on the individual segments of the working arm. The position and attitude of the tool can then be calculated from the inclinations of the individual arm segments via the known geometric relationships of the kinematic chain comprising, for example, adjustable boom, boom, shank and tool.
Since, however, sensors based on the measurement principle of inertia such as, for example, gravitation-sensitive pendulums, are used as inclination sensors, they are frequently also sensitive to accelerations due to shocks and vibrations such as occur unavoidably when such work machines are used. Such motion-induced accelerations can substantially disturb or temporarily disable the measurement of the position and attitude of the tool. A known measure for suppressing these disturbances consists of a lowpass filtering of the sensor signals such that motion-induced accelerations outside the useful frequency band are suppressed.
However, this is attended by a number of disadvantages: firstly, accelerations within the useful frequency band cannot be suppressed in this way, while secondly the lowpass filtering causes a temporal delay of up to a few hundred milliseconds which is, however, accepted, because it still enables an adequately accurate position display and does not hinder the manual operation of the working arm.
It is known from other technical fields to make use of a combination of acceleration-based inclination and rotation rate sensors to control the position of, for example, a robot, an aerodynamic vehicle or a vehicle. WO 01/57474 A1 discloses such a method, in which a quaternion representation is used to calculate a position.